Field of the Invention
The invention relates to an antenna configuration of an apparatus for detecting a child safety seat placed on a seat of a motor vehicle.
Especially in light of recent findings regarding the apparent dangers posed by airbags and the development and integration of systems which will ensure proper inflation of airbags (i.e. adjusted inflation force depending on the occupant and/or temporary disengagement of the tripping mechanism), it is most important to dependably determine various bits of information regarding the type and position of any occupant on each motor vehicle seat exposed to such airbags. The information is particularly important when a child safety seat is placed on the vehicle seat.
There has become known from German Patent DE 44 09 971 C2 one such apparatus, in which one transmitting antenna and one receiving antenna each are disposed in the vehicle seat. An electromagnetic exciter field is broadcast periodically via the transmitting antenna. A resonator/transponder of a child safety seat placed on the passenger seat alters the exciter field in a characteristic way. The exciter field altered by the resonator is picked up as a measurement field by the receiving antenna and evaluated by an evaluation circuit. If a single characteristic for a resonator is ascertained in the measurement field, then an output circuit of the apparatus generates a status signal that is supplied in particular to an airbag controller. The airbag controller can vary the tripping of an airbag disposed in front of the vehicle seat, or a side airbag disposed laterally of the seat, on the basis of the status signal output by the child safety seat detection apparatus. Optionally, airbag tripping can be prevented, to protect a child in the child safety seat from the force of the airbag as it inflates.
An improvement of the foregoing system is disclosed in European Patent Disclosure EP 0 708 002. According to that disclosure it is possible not only to detect whether a child safety seat is disposed on the vehicle seat but also to ascertain the orientation of the child safety seat on the vehicle seat: Either the child safety seat is disposed in the travel direction on the passenger seat with its backrest toward the vehicle seat, or the child safety seat is disposed counter to the driving direction on the passenger seat with its backrest toward the dashboard. When child safety seats face forward, it may still be allowable under some circumstances for the airbag to be tripped. To detect the child safety seat orientation, a child safety seat has two resonators, one in its left half and the other in its right half. Correspondingly there are one transmitting antenna and one receiving antenna each disposed in the left and right halves of the vehicle seat. Each resonator alters the exciter field generated by the transmitting antennas in a different way, so that by an evaluation of the measurement fields picked up from the receiving antennas it can be detected which resonator is disposed above which half of the vehicle seat.
With such an antenna configuration, however, a child safety seat placed in skewed orientation on the vehicle seat cannot be detected, for instance where one resonator is located directly above a gap between the transmitting and receiving antennas in the middle of the vehicle seat and the other resonator is on the periphery of the vehicle seat. If the child safety seat is skewed in this way or rotated, and especially if it is placed transversely across the vehicle seat, in which case both resonators are located above the gap, then tripping of the airbag is just as dangerous as in the rear-facing orientation. Yet even so, the child safety seat detection apparatus would still furnish a status signal indicating the absence of a child safety seat. There would be no hindrance to tripping the airbag at its full strength.